Mechanisms and Materials for Alkaline Hydrogen Electrocatalysis

2017 Spring Symposium

Mau­reen Tang, Chem­i­cal and Bio­log­i­cal Engi­neer­ing, Drex­el Uni­ver­si­ty, Philadel­phia, PA

Abstract — Hydro­gen is a poten­tial low cost, scal­able ener­gy stor­age medi­um for renew­able elec­tric­i­ty gen­er­a­tion. More impor­tant­ly, study of the hydro­gen elec­trode reac­tions has led to the dis­cov­ery of many of the fun­da­men­tal con­cepts in elec­tro­chem­istry and elec­tro­catal­y­sis. It has long been rec­og­nized that the reac­tion rates of the hydro­gen oxi­da­tion and hydro­gen evo­lu­tion reac­tions (HOR and HER) are slow­er in basic than acidic elec­trolytes, even though the sur­face inter­me­di­ate of adsorbed hydro­gen is inde­pen­dent of solu­tion pH. Under­stand­ing the root of this obser­va­tion is crit­i­cal to design­ing cat­a­lysts for a mul­ti­tude of elec­tro­chem­i­cal reac­tions with rel­e­vance to ener­gy con­ver­sion and stor­age. In this work, we under­take both applied and fun­da­men­tal efforts to under­stand the mech­a­nisms and devel­op low-cost, active cat­a­lysts for the hydro­gen reac­tions in base.

In the first part of the talk, we uti­lize a the­o­ry-guid­ed approach to devel­op nick­el-sil­ver cat­a­lysts for alka­line hydro­gen evo­lu­tion and oxi­da­tion. Den­si­ty-func­tion­al-the­o­ry cal­cu­la­tions pre­dict these alloys will be active for hydro­gen evo­lu­tion and oxi­da­tion. To cir­cum­vent the ther­mo­dy­nam­ic insol­u­bil­i­ty of these two met­als and iso­late cat­alyt­ic activ­i­ty, we employ an uncom­mon phys­i­cal vapor code­po­si­tion syn­the­sis. Our mea­sure­ments show that the alloy is indeed more active for hydro­gen evo­lu­tion than pure nick­el. In the sec­ond part of the talk, we exam­ine specif­i­cal­ly the hypoth­e­sis that water ori­en­ta­tion gov­erns the rate of hydro­gen adsorp­tion and thus the over­all HER/HOR kinet­ics by mod­u­lat­ing the poten­tial of zero charge of oxide sup­ports in acid and base. Final­ly, we com­bine micro­ki­net­ic mod­el­ing and sin­gle-crys­tal mea­sure­ments to deter­mine if adsorbed hydrox­ide func­tions as an active inter­me­di­ate or spec­ta­tor in the reac­tion. The results of these stud­ies high­light the impor­tance of kinet­ic bar­ri­ers, as well as adsorp­tion ener­gies, and con­tribute to resolv­ing a long-stand­ing para­dox in elec­tro­catal­y­sis and sur­face sci­ence.

Biog­ra­phy — Mau­reen Tang joined the fac­ul­ty of Chem­i­cal and Bio­log­i­cal Engi­neer­ing at Drex­el Uni­ver­si­ty in Fall 2014. She received her B.S. in Chem­i­cal Engi­neer­ing from Carnegie Mel­lon Uni­ver­si­ty and her Ph. D. from the Uni­ver­si­ty of Cal­i­for­nia, Berke­ley. While at Berke­ley, she received a NSF Grad­u­ate Research Fel­low­ship, an NSF East Asia Pacif­ic Sum­mer Fel­low­ship, and the Daniel Cubi­ciot­ti Stu­dent Award of the Elec­tro­chem­i­cal Soci­ety. Dr. Tang has com­plet­ed post­doc­tor­al work at Stan­ford Uni­ver­si­ty and research intern­ships at Kyoto Uni­ver­si­ty, the Uni­ver­si­ty of Dort­mund, and Dupont. Her research at Drex­el devel­ops mate­ri­als, archi­tec­tures, and fun­da­men­tal insight for elec­tro­chem­i­cal ener­gy stor­age and con­ver­sion.